Many projection systems incorporate small image modulators that use relatively small light sources, which are commonly referred to as “point” sources. Examples of point sources include a laser and short-arc lamp. These small sources are generally used to maximize the amount of light which can be applied to a small image source or light valve. One common approach is to use short-arc, high intensity discharge lamps. While short-arc, high intensity discharge lamps have many desirable properties, some of the associated attributes make such lamps difficult to use. For example, arc lamps may not be desirable for use in heads-up displays (HUD), as well as avionics display designs in general. The thermal output and shorter lifetime typically associated with arc lamps make the arc lamps less than ideal for HUD applications. HUD design considerations additionally favor image sources that are not as small as those typically used in commercial projection systems. In addition, HUD applications present a further challenge of providing substantially high luminance.
One attractive light source is a fluorescent lamp. Fluorescent lamps are commonly used in avionics displays and have a relatively longer lifetime with relatively high efficiency. However, obtaining high luminance values that are generally needed for HUD systems is difficult using fluorescent lamps. One approach to address this shortcoming is to use aperture lamps. To increase luminance, aperture lamps use fluorescent lamps with each fluorescent lamp having a cavity construction forming an aperture to emit light. For example, a portion of a fluorescent tube may be covered with phosphor, and a remaining portion of the tube has a thin or absent layer of phosphor to form a relatively narrow region for emitting light therethrough. With aperture lamps, the light source appears as a narrow light-emitting stripe on a larger body and generally lacks uniformity of light output. A diffuser may be used to obtain a more uniform light output, but generally has a significant negative impact on system efficiency. Multiple aperture lamps aligned in parallel may also be used to backlight avionics displays while maintaining longer lifetime and relatively high efficiency, but gaps reside between the lit apertures and generally create non-uniformity.
Accordingly, it is desirable to provide a backlight for displays having high luminance, improved uniformity, and efficiency of light output. In addition, it is desirable to provide an extended light source having improved uniformity and efficiency of light output. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.